Water contamination of Lithium Ion Battery (LIB) electrolytes leads to hydrofluoric (HF) acid formation¹, which impacts the formation² and degradation³ of the SEI layer as well as causing corrosion of the positive electrode oxide materials and inactive components of the cell⁴. One of the inactive components that corrodes is the Ni-coated steel can used in the commercial 18650 cells. This paper presents for the first time a detailed report of Ni corrosion in water-contaminated organic-based LiPF₆ electrolytes. The study reveals the chemical and electrochemical nature of Ni corrosion. Cyclic voltammetry, chronoamperometry and Tafel analysis coupled with electrochemical quartz microbalance (EQCM) technique were used to investigate the mechanism of the Ni dissolution at OCV and near OCV potentials (2.5 V – 3.5 V vs. Li/Li⁺). Chronoamperometry at a potential close to OCV gives a current and mass plateau for the first few hours (4 – 6 h) followed by a sudden oxidation current and mass loss due to Ni dissolution (Figure 1) indicating the generation of electrolyte-soluble corrosive species, which was confirmed by testing a pristine Ni electrode in the same used electrolyte (Figure 1). Speciation of dissolved Ni and generated corrosive species is of the great importance for revealing the mechanism and is in the focus of the ongoing research. SEM reveals pitting corrosion of Ni in LiPF₆ based electrolytes.

References

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2. D. Strmcnik et al., Nat. Catal., 1, 255–262 (2018).
3. J. G. Han et al., J. Power Sources, 446, 227366 (2020).
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Figure 1. Three-electrode EQCM: Ni electrode mass change in 0.25 % water spiked 1 M LiPF₆/EC/DEC (1:1) electrolyte during chronoamperometry at 3.35 V vs. Li/Li⁺.